InfinityFree主机环境下PHPMailer发送邮件报HTTP 500错误的问题求助

我在InfinityFree主机上部署的网站，用PHPMailer发送邮件时遇到了HTTP 500错误，没有其他额外的错误提示信息。我反复检查了代码，但还是没法定位问题出在哪里。

我的代码逻辑是当用户提交邮箱地址后，调用PHPMailer发送对应类型的相册访问邮件，所有代码都放在同一个文件中，完整内容如下：

require 'phpmailer/vendor/autoload.php';
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

function send_live_album_email($email, $album_url, $qr_code_file) {
    return send_qr_email($email, $album_url, $qr_code_file, "Live Album Access");
}

function send_longterm_album_email($email, $album_url) {
    $qr_code_file = "";
    return send_qr_email($email, $album_url, $qr_code_file, "Long-term Album Access");
}

function send_qr_email($email, $album_url, $qr_code_file) {
    $mail = new PHPMailer(true);
    $mail->IsSMTP();
    $mail->SMTPDebug = 0;
    $mail->SMTPAuth = true;
    $mail->SMTPSecure = "tls";
    $mail->Port = 587;
    $mail->Host = "smtp.gmail.com";
    $mail->Username = "my_email"; // 邮箱已打码
    $mail->Password = "my_password"; // 密码已打码
    $mail->IsHTML(true);
    $mail->AddAddress($email);
    $mail->setFrom("my_email", "Photo Album Access | Photographer App");
    // 邮件主题和内容
    $mail->Subject = "Photographer | Photo Album QR Code";
    $qr_code_image_url = "url_here" . htmlspecialchars($qr_code_file ?? ''); // URL已打码
    $email_template = "
        <h2>Hello!</h2>
        <p>Here is your link to access the photo album:</p>
        <p><a type='button' class='btn btn-primary' href='$album_url'>Click here to view album</a></p>
        <br><br>
        <p>Regards,</p>
        <h4>Photographer App</h4>
    ";
    $mail->Body = $email_template;
    $mail->AltBody = strip_tags($email_template);
    try {
        $mail->send();
        return true;
    } catch (Exception $e) {
        return false;
    }
}

if (isset($_POST['send_email'])) {
    $email = filter_var($_POST['email'], FILTER_SANITIZE_EMAIL);
    $album_url = "url_here"; // URL已打码
    if ($isLive) {
        if ($qr_code_file) {
            if (send_live_album_email($email, $album_url, $qr_code_file)) {
                echo "<script>alert('Live album sent successfully!');</script>";
            } else {
                echo "<script>alert('Failed to send live album email.');</script>";
            }
        } else {
            echo "<script>alert('QR code not available for live album.');</script>";
        }
    } else {
        if (send_longterm_album_email($email, $album_url)) {
            echo "<script>alert('Album email sent successfully!');</script>";
        } else {
            echo "<script>alert('Failed to send long-term album email.');</script>";
        }
    }
}
?>

<form action="" method="post">
    <div class="mb-3">
        <label for="email" class="form-label">Email</label>
            <input type="email" name="email" id="email" class="form-control" placeholder="Enter your email here" required>
    </div>
    <button name="send_email" type="submit" class="btn btn-primary">Submit</button>
</form>

备注：内容来源于stack exchange，提问作者krxshia